FIG. 1 schematically illustrates a typical prior-art scenario 100 of a surveyor 105 using a cooperative target 110 with a robotic total station 115 mounted on a tripod 120. The robotic total station 115 can also be used with non-cooperative targets to measure their positions. The robotic total station 115 has a telescope with a coaxial electronic-distance measurement (EDM) system for measuring a distance 125 to the target 110. The robotic total station may be remotely controlled via a communication channel 130. The telescope is aimed by rotation in a vertical direction 135 about a first axis (not shown in FIG. 1) and azimuthally about a second axis 140.
The elevation and azimuth of the telescope are recorded along with the distance measurement when the telescope axis is aimed at a target location. The optical axis of the telescope and EDM is rotated about one or both of the rotation axes to shift from one target location to another.
FIG. 2 schematically illustrates a typical prior-art scenario 200 of a 3D laser scanner 205 mounted on a tripod 210 for taking measurements of a scene such as a building 215 and surroundings 220 to obtain a 3D cloud of measured points over vertical and azimuthal angular limits indicated by dashed lines 225, 230, 235, 240. The scanner 205 typically has a rotating mirror to scan the optical axis of the instrument (i.e. the EDM axis) at a high speed in a vertical direction 245. The rotating mirror is mounted on a scan head rotating azimuthally about an axis 250 at low speed.
The EDM of the scanner 205 is free-running at a high repetition rate, and is not aimed at specific target locations. The elevation and azimuth of the telescope are recorded along with each distance measurement.
The azimuth angle, elevation angle and distance measurements of the scanner 205 are not as precise as those of a total station such as the total station 115 of FIG. 1, and the EDM beam is not aimed at specific target locations. The total station 115 has the advantage of greater measurement precision than the scanner 205, while the scanner 205 has the advantage of acquiring point measurements at a much higher repetition rate than the total station 115.
FIG. 3 schematically illustrates a prior-art scenario 300 of a surveyor 305 using a target 310 with a robotic total station 315 mounted on a tripod 320. In a first mode, the surveyor 305 may use the total station 315 to perform distance measurements to the specific target 310 mounted on a pole hold by the surveyor 305, as already illustrated in FIG. 1. In a second mode (or scanning mode), the total station 315 may be used to acquire a 3D cloud of point measurements of a scene such as a building 325 and surroundings 330. Dashed lines 335, 340, 345, 350 indicate the vertical and azimuthal angular limits of the measurement when the total station 315 is used in this second, scanning mode. Acquiring a dense cloud of point measurements with a total station as in FIG. 3 is usually slow and cumbersome, as the telescope must be repositioned for each measured point.
Another type of prior-art scanning total station may have the telescope rotating continuously while distance measurements are acquired at a fairly high rate (about 1000 Hz). This design is still limited by the large inertia of the telescope.